You have to connect your iPad to your computer and restore it in iTunes. I have provided the following link.
If you set up a passcode again, write the 4 digit code down somewhere safe for easy recall.........
There is only one way. You have to restore the iPad. You will probably need to use recovery mode.
You have to restore the device within iTunes. You want to use the same computer that you always sync with so that you can restore your app data and settings. You can restore with any other computer, but you will lose everything on the iPad.
IOS: Wrong passcode results in red disabled screen
This will tell you how to restore
If you cannot restore that way, you may have to use recovery mode
1: Connect the device to your computer and open iTunes.
2: If the device appears in iTunes, select and click Restore on the Summary pane.
3: If the device doesn't appear in iTunes, try using the steps in this article to force the device into recovery mode.